The present invention relates generally to an imaging system, and specifically to an imaging system comprising a zoom lens and an electronic image pickup device such as a CCD. More specifically, the present invention is concerned with a digital camera capable of obtaining electronic images.
So far, imaging systems incorporating a zoom lens and an electronic image pickup device, for the most part, have made use of a so-called variable stop with variable aperture diameter to control the quantity of light passing through the zoom lens.
Current image pickup devices, on the other hand, are designed with an increasing number of pixels for the purpose of achieving image quality improvements.
The more the number of pixels in an image pickup device, the higher the optical performance demanded for an optical system becomes. A problem with the use of the conventional variable stop is, however, that when it is intended to diminish the stop diameter for light quantity control, resolution drops due to the influence of diffraction. It is thus difficult to make any sensible tradeoff between light quantity control and image quality improvements.
Even when it is desired to cut down the length of the zoom lens, the thickness of the variable stop due to its mechanical makeup often imposes limitations on reducing the length of the optical system.